CN109133433B - Organic pollution blockage control method for reverse osmosis membrane - Google Patents

Organic pollution blockage control method for reverse osmosis membrane Download PDF

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CN109133433B
CN109133433B CN201811210475.8A CN201811210475A CN109133433B CN 109133433 B CN109133433 B CN 109133433B CN 201811210475 A CN201811210475 A CN 201811210475A CN 109133433 B CN109133433 B CN 109133433B
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water
activated carbon
concentration
ferric chloride
adding concentration
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CN109133433A (en
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胡洪营
巫寅虎
白苑
方品晟
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Tsinghua University
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/08—Prevention of membrane fouling or of concentration polarisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/16—Use of chemical agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/21—Dissolved organic carbon [DOC]
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/14—Maintenance of water treatment installations

Abstract

The invention discloses an organic pollution blockage control method of a reverse osmosis membrane, which preliminarily determines the adding proportion of activated carbon and ferric chloride according to the measurement results of the molecular weight of organic matters in an inlet water sample and a three-dimensional fluorescence spectrogram thereof; determining the adding concentration intervals of the activated carbon and the ferric chloride according to the DOC concentration, respectively obtaining corresponding DOC removal rates, determining the optimal activated carbon adding concentration A and the optimal ferric chloride adding concentration B according to the minimum dosage value required for stably removing the DOC, adding the activated carbon with the concentration A into the reverse osmosis inlet water, adsorbing for 0.5-1 hour, then adding the ferric chloride with the concentration B, and removing the activated carbon and the residual organic matters through coagulation. The method has the characteristics of low cost, low energy consumption, simple operation and the like, and achieves the purposes of stabilizing the water quality of the inlet water of the RO system, slowing down the pollution and blockage rate of the RO system and increasing the running stability and running time of the RO system by removing organic pollutants in the inlet water of the RO system, thereby reducing the running cost of the RO system.

Description

Organic pollution blockage control method for reverse osmosis membrane
Technical Field
The invention relates to the technical field of reverse osmosis desalination of reclaimed water, in particular to an organic fouling control method of a reverse osmosis membrane.
Background
The water resource in China is seriously in short supply, the sewage recycling is an effective way for solving the problem, the utilization of the recycled water is fully developed, and the method has very important significance for relieving the water resource shortage in China. Reverse Osmosis (RO) is gradually applied to the field of sewage regeneration due to good water quality and stable operation of produced water, but organic matters in sewage can cause serious pollution and blockage of an RO membrane, so that the water yield and the water quality of the RO system are reduced, the operation energy consumption and the cost are increased, and the popularization of the RO process is limited.
Most municipal domestic sewage regenerated water plants can increase a series of pretreatment processes before RO system main body processes, and organic pollutants in RO system inlet water can be removed through the pretreatment modes, so that the purposes of stabilizing the RO system inlet water quality, slowing down the RO system pollution and blockage rate, increasing the RO system operation stability and operation time and reducing the RO system operation cost are achieved.
Common pretreatment processes include: coagulating sedimentation, activated carbon filtration, microfiltration/ultrafiltration and the like, wherein the coagulating sedimentation and activated carbon processes are widely applied due to low cost and simple operation, but the pretreatment processes are usually used independently and are not combined, the research on the removal condition of components of organic matters in inlet water by combining different pretreatment processes is very lacking, and a specific method for combining the pretreatment processes is not used, so that how to design a combined pretreatment process to further slow down the fouling rate of an RO system has important significance in the aspects of controlling organic fouling of an RO membrane and the like.
Disclosure of Invention
In order to solve the problems, the invention aims to provide an organic fouling control method based on ferric chloride coagulating sedimentation and granular activated carbon combined pretreatment before a main process of a reverse osmosis system, which is used for controlling organic fouling of a reverse osmosis membrane.
The invention is realized by the following technical scheme: an organic fouling control method for a reverse osmosis membrane comprises the following steps:
(1) preparing two water treatment agents, namely ferric chloride stock solution and clean active carbon;
(2) taking an inlet water sample out of target inlet water of the reverse osmosis membrane, dividing the water sample into a plurality of parts, respectively adding activated carbon and ferric chloride to different concentrations, obtaining the removal rate of soluble organic carbon (DOC) in the corresponding water sample under different adding concentrations of the activated carbon and the ferric chloride, and determining the optimal adding concentration A of the activated carbon and the optimal adding concentration B of the ferric chloride according to the adding concentration and the DOC removal rate, wherein the adding concentration is the concentration of a water treatment agent in the water sample after the water treatment agent is added to the water sample;
(3) and (3) according to the optimal adding concentration of the activated carbon and the ferric chloride determined in the step (2), adding the activated carbon into the target inlet water to enable the concentration of the activated carbon in the target inlet water to be A, adsorbing for 0.5-1 hour, then adding the ferric chloride into the target inlet water to enable the concentration of the ferric chloride in the target inlet water to be B, and removing the activated carbon and the residual organic matters through coagulation.
According to the method, active carbon and ferric chloride are added into a water sample, DOC removal rates of the active carbon and the ferric chloride under different adding concentrations are obtained, the optimal adding concentration of the active carbon and the ferric chloride is determined according to the DOC removal rates, and then the active carbon and the ferric chloride are sequentially added into target inlet water to enable the concentration of the active carbon and the ferric chloride in the target inlet water to be the optimal adding concentration; the purpose of determining the optimal adding concentration is to select the minimum dosage of the water treatment agent while ensuring the stable removal of DOC, so that the removal efficiency of organic matters is highest, the economic benefit is improved, the adding concentration is too large or too small, the DOC removal rate cannot be in a higher stable state, the water quality meeting the requirement cannot be achieved, and when the adding concentration is too large, the adding dosage of the water treatment agent is higher, and the economic benefit cannot be maximized; the activated carbon can be used as an adsorbent to adsorb a part of organic matters in the sewage firstly, the adsorption performance is gradually reduced after 0.5-1 hour of adsorption, and then ferric chloride is added as a coagulant to remove the residual organic matters and simultaneously coagulate and remove the redundant activated carbon, so that the treatment steps of the activated carbon are reduced.
The invention adopts the combined pretreatment mode of ferric chloride coagulating sedimentation and granular activated carbon, compared with the condition that the ferric chloride coagulating sedimentation and the granular activated carbon are independently pretreated, the removal rate of organic matters is improved, and the reduction speed of the water production rate is smaller than the condition that the two pretreatment modes are independently used along with the extension of the running time, thereby further prolonging the service life of the reverse osmosis membrane and improving the water quality of the produced water.
The method has the characteristics of low cost, low energy consumption, simple operation and the like, and achieves the purposes of stabilizing the water quality of the inlet water of the RO system, slowing down the pollution and blockage rate of the RO system and increasing the running stability and running time of the RO system by removing organic pollutants in the inlet water of the RO system, thereby reducing the running cost of the RO system.
Preferably, in step (1), the preparation and storage method of the ferric chloride stock solution is as follows: storing ferric chloride in a closed bottle, preparing a ferric chloride stock solution with the concentration of 1g/L at room temperature as a coagulant, and storing in a dark sealed manner after preparation.
Because the ferric chloride is added in the concentration of the water sample in the subsequent step, the concentration of 1g/L is selected, so that the ferric chloride is convenient to dilute in the subsequent addition; in order to prevent the influence of moisture in the air on the ferric chloride stock solution, the ferric chloride stock solution is stored in a sealed mode, and in order to prevent the influence of light on the temperature of the ferric chloride solution, further causing the deterioration of the ferric chloride, the ferric chloride stock solution is stored in a light-proof mode.
Preferably, in step (1), the preparation and storage method of the activated carbon comprises the following steps: coconut shell granular activated carbon with the grain size of 1-2mm is adopted, the activated carbon needs to be repeatedly washed by water before being used until the effluent water of the washed activated carbon Dissolves Organic Carbon (DOC) less than 0.5mg/L, and then the clean activated carbon can be prepared; the clean active carbon is placed in an oven at 70 ℃ for drying, and then is placed in a beaker for light-tight sealing and storage.
In the step (2), determining the initial DOC concentration value a in the influent water sample0mg/L, determining the adding concentration of a water treatment agent in the water inlet sample as biThe corresponding DOC concentration value at mg/L is aimg/L, the adding concentration of the water treatment agent is biDOC removal rate c corresponding to mg/LiComprises the following steps: (a)i-a0)/a0。
Preferably, in step (2), the DOC concentration is determined by the following method: 5ml of water sample to be detected is taken, and the DOC concentration in the water sample is determined by using a TOC analyzer after the water sample passes through a 0.45 mu m filter membrane.
Preferably, in step (2), the method for determining the optimal dosing concentration is as follows: selecting the corresponding adding concentration of the water treatment agent as the optimal adding concentration when the ratio of the increasing rate of the relative DOC removing rate to the increasing rate of the relative adding concentration of the water treatment agent is closest to 1; suppose that two adjacent adding concentrations of the same water treatment agent are respectively bi-1、bi(bi>bi-1) The respective DOC removal rates are ci-1、ciIf the adding concentration of the water treatment agent is biWhen the DOC removal rate is increased, the DOC removal rate is (c)i-ci-1)/ci-1The increase rate of the addition concentration of the water treatment agent is (b)i-bi-1)/bi-1。
Further preferably, in the step (2), firstly determining the adding concentration interval of the activated carbon and the ferric chloride, and then determining the optimal adding concentration in the adding concentration interval;
the determination method of the adding concentration interval comprises the following steps: determining the initial DOC concentration value in the influent water sample as a0mg/L, the adding concentration area of the activated carbon and the ferric chlorideBetween each other is (3-9). a0mg/L and (1-9) × a0mg/L. The concentration interval here is an optimal DOC removal interval, and the DOC removal rate at this time can be maximized.
Further preferably, in the step (2), the adding concentration of the activated carbon is 3a0mg/L、4.5a0mg/L、6a0mg/L、7.5a0mg/L、9a0mg/L. Further preferably, in the step (2), the optimal adding concentration ratio of the activated carbon and the ferric chloride is determined, and then the adding concentration of the ferric chloride is determined according to the optimal adding concentration ratio and the adding concentration of the activated carbon;
preferably, the determination method of the optimal dosing concentration ratio comprises the following steps: measuring the molecular weight of organic matters in the reverse osmosis influent water sample, determining and obtaining a three-dimensional fluorescence spectrogram of the reverse osmosis influent water sample, and judging whether the water sample has (1) the molecular weight of 102-103An obvious absorption peak in a Da range and (2) obvious fluorescence response in an IV region and a VI region in a three-dimensional fluorescence spectrum; if the characteristics of the two water samples are both possessed, the optimal adding concentration ratio of the activated carbon to the ferric chloride in the water inlet water sample is determined to be 1: 1; if the water sample only has the characteristics of one water sample, determining that the optimal adding concentration ratio of the water sample to the water sample is 2: 1; if the characteristics of the two water samples are not possessed, determining that the optimal adding concentration ratio of the two water samples is 3: 1.
preferably, in the step (2), another method for determining the optimal addition concentration A and the optimal addition concentration B comprises the following steps:
(21) determining the optimal adding concentration ratio of the activated carbon to the ferric chloride in the intake water sample according to the organic matter molecular weight characteristics and the three-dimensional fluorescence spectrogram characteristics of the intake water sample:
preferably, the polymer has (1) a molecular weight of 102-103The method comprises the following steps of (1) determining a water sample with an obvious absorption peak in a Da range and (2) an obvious fluorescence response in an IV area and a VI area in a three-dimensional fluorescence spectrum, wherein the two water samples have the characteristics, and determining the optimal adding concentration ratio of the two water samples in an inflow water sample to be 1: 1; if only one water sample characteristic is met, determining that the optimal adding concentration ratio of the water sample characteristic to the water sample characteristic is 2: 1; if none of the above characteristics are provided, determining twoThe optimal adding concentration ratio is 3: 1;
(22) determining the initial DOC concentration value of the influent water sample as a0mg/L, determining the adding concentration interval of the activated carbon in the water inlet sample to be (3-9). alpha.0mg/L, and obtaining the DOC removal rate in the water sample under different active carbon adding concentrations;
(23) determining the adding concentration interval of ferric chloride in the water inlet water sample according to the optimal adding concentration ratio determined in the step (21) and the adding concentration interval of the activated carbon in the step (22), and obtaining the removal rate of DOC in the water sample under different adding concentrations of the ferric chloride;
(24) and (4) selecting the corresponding water treatment agent addition concentration as the optimal addition concentration of the water treatment agent when the ratio of the DOC removal rate increase rate to the water treatment agent addition concentration is closest to 1 according to the DOC removal rates of different water treatment agents in the steps (22) and (23) under different addition concentrations.
In the step (3), the three-dimensional fluorescence spectrogram divides the three-dimensional fluorescence fingerprint map into 6 large areas according to the corresponding relation of typical fluorescent substances (amino acids, proteins, polysaccharides, humic acid-like substances and the like) in the inlet water of the reverse osmosis process of the municipal sewage regeneration system, wherein each area corresponds to different substances and respectively comprises the following steps: class i-tyrosine, tryptophan; class II tyrosine, tryptophan proteins; III-polysaccharides; IV-polycarboxylic humic acid substances; class V-polycyclic aromatic humic acids; VI-fulvic acid-like substances.
Drawings
FIG. 1 is a flow chart of a reverse osmosis membrane organic fouling control method provided by the invention;
FIG. 2 is a molecular weight distribution diagram of an influent water sample 1;
FIG. 3 is a three-dimensional fluorescence spectrum of the influent water sample 1;
FIG. 4 is a diagram showing the change of the water production rate of an inlet water sample 1 passing through a reverse osmosis membrane after being subjected to different pretreatment methods;
FIG. 5 is a graph showing the distribution of the molecular weight of an influent sample 2;
FIG. 6 is a three-dimensional fluorescence spectrum of an influent water sample 2;
FIG. 7 is a diagram showing the variation of the water production rate of an influent water sample 2 passing through a reverse osmosis membrane after being subjected to different pretreatment methods;
FIG. 8 is a graph showing the distribution of molecular weights of the influent sample 3;
FIG. 9 is a three-dimensional fluorescence spectrum of the influent water sample 3;
FIG. 10 is a diagram showing the variation of the water production rate of an influent water sample 3 passing through a reverse osmosis membrane after being subjected to different pretreatment methods;
FIG. 11 is a graph showing the distribution of molecular weights of influent sample 3;
FIG. 12 is a three-dimensional fluorescence spectrum of the influent water sample 3;
FIG. 13 is a graph showing the change of the water production rate of an incoming water sample 3 passing through a reverse osmosis membrane after different pretreatment methods.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The steps of the method for controlling organic fouling of a reverse osmosis membrane provided by the invention are shown in fig. 1, and are specifically described by the following examples, and the methods for preparing ferric chloride stock solution and cleaning activated carbon in different examples are the same.
The preparation and storage method of the ferric chloride stock solution comprises the following steps: storing ferric chloride in a closed bottle, preparing a ferric chloride stock solution with the concentration of 1g/L at room temperature as a coagulant, and storing in a dark sealed manner after preparation.
The preparation and storage method of the clean activated carbon comprises the following steps: coconut shell granular activated carbon with the grain size of 1-2mm is adopted, the activated carbon needs to be repeatedly washed by water before being used until the effluent water of the washed activated carbon Dissolves Organic Carbon (DOC) less than 0.5mg/L, and then the clean activated carbon can be prepared; the clean active carbon is placed in an oven at 70 ℃ for drying, and then is placed in a beaker for light-tight sealing and storage.
Firstly, preliminarily determining the adding proportion of activated carbon and ferric chloride by measuring the molecular weight of organic matters in a water sample and the measuring result of a three-dimensional fluorescence spectrogram; determining the adding concentration intervals of the activated carbon and the ferric chloride according to the DOC concentration, respectively obtaining corresponding DOC removal rates, determining the optimal activated carbon adding concentration A and the optimal ferric chloride adding concentration B according to the minimum dosage value required for stably removing the DOC, adding the activated carbon into the reverse osmosis inlet water to enable the adding concentration to be A, then adding the ferric chloride to enable the adding concentration to be B, and removing the activated carbon and the residual organic matters through coagulation.
When the optimal adding concentration is determined, the corresponding adding concentration interval when the DOC removal rate is high can be determined firstly, and then the optimal adding concentration is determined in the adding concentration interval, so that the selection times are reduced, and the test efficiency is improved; as the adding concentration interval has more point values and various value taking methods, the invention provides a method for taking values at even intervals, and the adding concentration of the activated carbon can be taken according to the initial concentration value a of DOC in the water sample0mg/L, and the adding concentration of the activated carbon is limited to be 3a0mg/L、4.5a0mg/L、6a0mg/L、7.5a0mg/L、9a0mg/L, the value taking method of the adding concentration is convenient and fast, and the DOC removal rate at the point value is also high.
In order to improve the efficiency of the combined treatment of the activated carbon and the ferric chloride and keep the addition amount of the activated carbon and the ferric chloride at a lower level as much as possible, the optimal adding concentration ratio of the activated carbon and the ferric chloride can be determined in advance, and the adding concentration of the ferric chloride can be determined according to the optimal adding concentration ratio and the adding concentration of the activated carbon; when the optimal adding concentration ratio is determined, the molecular weight of (1) 10 is selected2-103The two water samples have obvious absorption peaks in a Da range and (2) the three-dimensional fluorescence spectrum has obvious fluorescence response in an IV region and a VI region, the two water samples have simple and easy detection characteristics, wherein molecular weight shows the size of organic matter molecules in water, and the fluorescence spectrum characteristic shows the molecular structure (chemical functional group) of the organic matter in water. According to the characteristics of water samples of different target inflows, different optimal adding concentration ratios are selected, so that the standard water production rate of the target inflows is in a higher level, and for the same water sample, the standard water production rate increase rate when the optimal adding concentration ratio is selected is about 15-30% higher than the increase rate under other ratios, so that the pollution and blockage control effect is better.
Example 1
In the embodiment, the target inlet water 1 is adopted, and the method for controlling organic fouling in the reverse osmosis membrane inlet water 1 is determined as follows:
(1) preparing two water treatment agents, namely ferric chloride stock solution and clean active carbon;
(2) determining the optimal adding concentration A of the activated carbon and the optimal adding concentration B of ferric chloride:
(21) taking a water inlet sample 1 out of the reverse osmosis membrane target water inlet 1, measuring the molecular weight of organic matters in the reverse osmosis water inlet sample 1 by using a liquid chromatograph, wherein the molecular weight distribution diagram is shown in figure 2, and measuring and obtaining a three-dimensional fluorescence spectrogram of the reverse osmosis membrane water inlet sample 1 by using a fluorescence spectrophotometer, which is shown in figure 3; as can be seen from FIG. 2, the influent sample 1 is at 102-103As can be seen from FIG. 3, the water sample 1 has obvious fluorescence responses in the IV and VI regions, and thus, the optimal adding concentration ratio of the activated carbon to the ferric chloride in the water sample 1 is determined to be 1: 1;
(22) taking 5ml of a water sample to be detected, determining that DOC concentration of the water sample 1 is 4mg/L after the water sample passes through a 0.45-micron filter membrane, determining that the adding concentration of the activated carbon is 12mg/L, 18mg/L, 24mg/L, 30mg/L and 36mg/L, wherein the adding concentration refers to the concentration of the activated carbon in the water sample 1, dividing the water sample into a plurality of parts, respectively adding the activated carbon to the adding concentration, and obtaining the DOC removal rate of the water sample 1 under the adding concentration of the activated carbon, as shown in Table 1:
TABLE 1 removal rate of DOC in influent water sample 1 at different activated carbon addition concentrations
Figure BDA0001832335370000081
(23) Determining the adding concentration of ferric chloride (namely the concentration of ferric chloride in the inlet water sample 1) to be 12mg/L, 18mg/L, 24mg/L, 30mg/L and 36mg/L according to the optimal adding concentration ratio of the activated carbon to the ferric chloride in the step (21) and the adding concentration of the activated carbon in the step (22), dividing the inlet water sample into a plurality of parts, respectively adding the ferric chloride to the adding concentrations, and obtaining the DOC removal rate in the water sample 1 under the adding concentration of the ferric chloride, as shown in Table 2:
TABLE 2 removal rate of DOC in influent water sample 1 at different ferric chloride addition concentrations
Figure BDA0001832335370000082
(24) According to the DOC removal rate under different active carbon adding concentrations in the step (22), selecting the corresponding active carbon adding concentration of 24mg/L as the optimal adding concentration A of the active carbon when the ratio of the relative DOC removal rate increase rate to the relative active carbon adding concentration increase rate is closest to 1;
according to the DOC removal rate under different ferric chloride adding concentrations in the step (23), selecting the corresponding ferric chloride adding concentration of 18mg/L as the optimal adding concentration B of ferric chloride when the ratio of the relative DOC removal rate increase rate to the relative ferric chloride adding concentration increase rate is closest to 1;
(3) and (4) according to the optimal adding concentration of the activated carbon and the ferric chloride determined in the step (24), adding the activated carbon into the target inlet water 1 to enable the concentration of the activated carbon in the target inlet water 1 to be 24mg/L, adsorbing for 0.5 hour, then adding the ferric chloride to enable the concentration of the ferric chloride in the target inlet water 1 to be 18mg/L, and removing the activated carbon and the residual organic matters through coagulation.
The change of the normalized water production rate of the target inlet water 1 passing through the reverse osmosis membrane after the combined pretreatment of 24mg/L activated carbon and 18mg/L ferric chloride, the pretreatment of only 24mg/L activated carbon, the pretreatment of only 18mg/L ferric chloride and no pretreatment is shown in FIG. 4; as can be seen from fig. 4, in the operation process of the reverse osmosis membrane system, the water production rate of the combined pretreatment is higher than that of the other three modes, and the water production rate of the combined pretreatment is lower than that of the other three modes along with the increase of time, so that the effect of the combined pretreatment for controlling the fouling is more effective, stable and durable.
The normalized water production rates and normalized water production rate increase (compared to untreated water production rate) for each set of 30h runs in the 4 modes described above are shown in table 3 below:
TABLE 3 groups of influent samples 1 run for 30h in each pretreatment mode
Normalized water production rate and normalized water production rate enhancement rate
Figure BDA0001832335370000091
As can be seen from table 3, in the combined pretreatment mode, the normalized water production rate was higher when the combined pretreatment mode was operated for 30h than when the other two pretreatment modes were used alone, and the normalized water production rate was increased by 19.66% and 14.5% as compared to when activated carbon and ferric chloride were used alone, respectively.
In the above steps, the order of step (21) and step (22) may be reversed.
Example 2
In this embodiment, a target influent 2 is selected, and the organic fouling control method is the same as that in embodiment 1, except that:
the molecular weight distribution diagram of the organic matters in the influent water sample 2 is shown in FIG. 5, and the three-dimensional fluorescence spectrum diagram is shown in FIG. 6; as can be seen from FIG. 5, the influent sample 2 is at 103-104Water sample with obvious absorption peak in Da range and 102-103As can be seen from FIG. 6, the water sample 2 has significant fluorescence responses in the regions IV and VI, and thus the optimal adding concentration ratio of activated carbon to ferric chloride in the water sample 2 is determined to be 2: 1;
(ii) taking 5ml of a water sample to be detected, measuring the DOC concentration of the water sample 2 after the water sample to be detected passes through a 0.45-micron filter membrane to be 4mg/L, determining the adding concentration of the activated carbon to be 12mg/L, 18mg/L, 24mg/L, 30mg/L and 36mg/L according to the measuring result of the DOC, and obtaining the DOC removal rate of the water sample 2 under the adding concentration of the activated carbon, wherein the DOC removal rate is shown in Table 4:
TABLE 4 removal rate of DOC in influent water sample 2 at different activated carbon addition concentrations
Figure BDA0001832335370000101
According to the adding concentration of the activated carbon and the optimal adding concentration ratio of the activated carbon to the ferric chloride, the adding concentrations of the ferric chloride are determined to be 6mg/L, 9mg/L, 12mg/L, 15mg/L and 18mg/L, and the DOC removal rate in the water sample 2 under the adding concentration of the ferric chloride is obtained, and is shown in Table 5:
TABLE 5 removal rate of DOC in influent water sample 2 at different ferric chloride addition concentrations
Figure BDA0001832335370000111
According to DOC removal rates of different activated carbon adding concentrations in the table 4, selecting the corresponding activated carbon adding concentration of 18mg/L as the optimal adding concentration A when the ratio of the relative DOC removal rate increase rate to the relative activated carbon adding concentration increase rate is closest to 1; according to DOC removal rates of different ferric chloride adding concentrations in the table 5, selecting the corresponding ferric chloride adding concentration of 12mg/L as the optimal adding concentration B when the ratio of the relative DOC removal rate increase rate to the relative ferric chloride adding concentration increase rate is closest to 1;
(iii) according to the determined optimal adding concentration of the activated carbon and the ferric chloride, adding the activated carbon into the target inlet water 2 to enable the concentration of the activated carbon in the target inlet water 2 to be 18mg/L, adsorbing for 1 hour, then adding the ferric chloride to enable the concentration of the ferric chloride in the target inlet water 2 to be 12mg/L, and removing the activated carbon and the residual organic matters through coagulation.
The normalized water production rate change through the reverse osmosis membrane for the target feed water 2 pretreated with a combination of 18mg/L activated carbon and 12mg/L ferric chloride, after pretreatment with only 18mg/L activated carbon, pretreatment with only 12mg/L ferric chloride, and without any pretreatment is shown in FIG. 7.
The normalized water production rates and normalized water production rate increases for each set of 30h runs in the 4 modes described above are shown in table 6 below:
TABLE 6 standardized Water production Rate and standardized Water production Rate improvement Rate for each set of influent Water sample 2 when run for 30h under each pretreatment mode
Figure BDA0001832335370000121
As can be seen from table 6, in the combined pretreatment mode, the normalized water production rate was higher than the water production rates of the other two pretreatment modes when operated for 30h, and the water production rate was increased by 24.48% and 17.28% compared to the activated carbon and ferric chloride when used alone.
Example 3
The target inflow 3 is adopted in the embodiment, and the organic fouling control method is the same as that of the embodiment 1, and the difference is that:
the molecular weight distribution diagram of the organic matters in the influent water sample 3 is shown in FIG. 8, and the three-dimensional fluorescence spectrum diagram is shown in FIG. 9; as can be seen from FIG. 8, the influent sample 3 is at 102-103As can be seen from FIG. 9, the water sample 3 has significant fluorescence responses in the regions I and II, but no significant fluorescence responses in the regions IV and VI, so as to determine that the optimal adding concentration ratio of the activated carbon to the ferric chloride in the water sample 3 is 2: 1;
(ii) taking 5ml of a water sample to be detected, measuring the DOC concentration of the inlet water sample 3 to be 6mg/L after passing through a 0.45-micron filter membrane, determining the adding concentration of the activated carbon to be 18mg/L, 27mg/L, 36mg/L, 45mg/L and 54mg/L according to the measuring result of the DOC, and obtaining the DOC removal rate in the water sample under the adding concentration of the activated carbon, as shown in Table 7:
TABLE 7 removal rate of DOC in influent water sample 3 at different activated carbon addition concentrations
Figure BDA0001832335370000131
According to the adding concentration of the activated carbon and the optimal adding concentration ratio of the activated carbon to the ferric chloride, the adding concentrations of the ferric chloride are determined to be 9mg/L, 13.5mg/L, 18mg/L, 22.5mg/L and 27mg/L, and the DOC removal rate in the water sample under the adding concentrations of the ferric chloride is obtained, as shown in Table 8:
TABLE 8 removal rate of DOC in influent water sample 3 at different ferric chloride addition concentrations
Figure BDA0001832335370000132
According to DOC removal rates of different activated carbon adding concentrations in the table 7, when the ratio of the relative DOC removal rate increase rate to the relative activated carbon adding concentration increase rate is closest to 1, the corresponding activated carbon adding concentration of 27mg/L is selected as the optimal adding concentration A; according to DOC removal rates of different ferric chloride adding concentrations in the table 8, selecting the corresponding ferric chloride adding concentration of 13.5mg/L as the optimal adding concentration B when the ratio of the relative DOC removal rate increase rate to the relative ferric chloride adding concentration increase rate is closest to 1;
(iii) adding activated carbon into the target inlet water 3 according to the determined optimal adding concentration of the activated carbon and the ferric chloride to enable the concentration of the activated carbon in the target inlet water 3 to be 27mg/L, adsorbing for 0.75 hour, adding the ferric chloride to enable the concentration of the ferric chloride in the target inlet water 3 to be 13.5mg/L, and removing the activated carbon and the residual organic matters through coagulation.
The normalized water production rate through the reverse osmosis membrane for the target feed water 3 pretreated with a combination of 27mg/L activated carbon and 13.5mg/L ferric chloride, after pretreatment with only 27mg/L activated carbon, pretreatment with only 13.5mg/L ferric chloride, and no pretreatment is shown in FIG. 10.
The normalized water production rates and normalized water production rate increases for each set of 30h runs in the 4 modes described above are shown in table 9 below:
TABLE 9 standardized Water production Rate and standardized Water production Rate improvement rates for groups of influent Water samples 3 operating for 30 hours in each pretreatment mode
Figure BDA0001832335370000141
As can be seen from table 9, in the combined pretreatment mode, the normalized water production rate was higher than the water production rates of the other two pretreatment modes when operated for 30h, and the water production rate was increased by 16.18% and 20.51% compared to the activated carbon and ferric chloride when used alone, respectively.
Example 4
The target inflow water 4 is adopted in the embodiment, and the organic pollution blockage control method is the same as that of the embodiment 1, and the difference is that:
the distribution diagram of the molecular weight of the organic matters in the influent water sample 4 is shown in FIG. 11, and the three-dimensional fluorescence spectrum thereof is shown in FIG. 12; as can be seen from FIG. 11, the influent sample 4 is at 103-104Water sample with obvious absorption peak in Da range and 102-103As can be seen from FIG. 12, the water sample 4 has an obvious fluorescence response in region V and no fluorescence response in regions IV and VI, so that the optimal adding concentration ratio of activated carbon to ferric chloride in the water sample 4 is determined to be 3: 1;
(ii) taking 5ml of a water sample to be detected, determining that the DOC concentration of the inlet water sample 4 is 5mg/L after the water sample passes through a 0.45-micron filter membrane, determining the adding concentrations of the activated carbon to be 15mg/L, 22.5mg/L, 30mg/L, 37.5mg/L and 45mg/L according to the DOC determination result, and obtaining the DOC removal rate in the water sample under the adding concentrations of the activated carbon, wherein the DOC removal rate is shown in Table 10:
TABLE 10 removal rate of DOC in influent water sample 4 at different activated carbon addition concentrations
Figure BDA0001832335370000151
According to the adding concentration of the activated carbon and the optimal adding concentration ratio of the activated carbon to the ferric chloride, the adding concentration intervals of the ferric chloride are determined to be 5mg/L, 7.5mg/L, 10mg/L, 12.5mg/L and 15mg/L, and the DOC removal rate in the water sample under the adding concentration of the ferric chloride is obtained, as shown in Table 11:
TABLE 11 removal rate of DOC in influent water sample 4 at different ferric chloride addition concentrations
Figure BDA0001832335370000152
According to DOC removal rates of different activated carbon adding concentrations in the table 10, the corresponding activated carbon adding concentration of 22.5mg/L is selected as the optimal adding concentration A when the ratio of the relative DOC removal rate increase rate to the relative activated carbon adding concentration increase rate is closest to 1; according to DOC removal rates of different ferric chloride adding concentrations in the table 11, selecting the corresponding ferric chloride adding concentration of 10mg/L as the optimal adding concentration B when the ratio of the relative DOC removal rate increase rate to the relative ferric chloride adding concentration increase rate is closest to 1;
(iii) according to the determined optimal adding concentration of the activated carbon and the ferric chloride, adding the activated carbon into the target inlet water 4 to enable the concentration of the activated carbon in the target inlet water 4 to be 22.5mg/L, adsorbing for 0.8 hour, then adding the ferric chloride to enable the concentration of the ferric chloride in the target inlet water 4 to be 10mg/L, and removing the activated carbon and the residual organic matters through coagulation.
The normalized water production rate through the reverse osmosis membrane for the target feed water 4 pretreated with a combination of 22.5mg/L activated carbon and 10mg/L ferric chloride, after pretreatment with only 22.5mg/L activated carbon, pretreatment with only 10mg/L ferric chloride, and no pretreatment is shown in FIG. 13.
The normalized water production rates and normalized water production rate increase rates for each set of 30h runs in the 4 modes described above are shown in table 12 below:
TABLE 12 run of influent sample 4 for 30h in each pretreatment mode
Normalized water production rate and normalized water production rate enhancement rate
Figure BDA0001832335370000161
As can be seen from table 12, in the combined pretreatment mode, the normalized water production rate was higher than the water production rates of the other two pretreatment modes when operated for 30h, and the water production rate was increased by 34.15% and 52.88% compared to the activated carbon and ferric chloride when used alone, respectively.
As can be seen from fig. 4, 7, 10 and 13 in the above embodiments, after the pretreatment is added, the reduction of the water production rate is slowed down, which indicates that organic matters in the water sample are partially removed, and the fouling of the reverse osmosis membrane is reduced, wherein the organic matters in the inlet water can be further removed when the activated carbon and the ferric chloride are used in combination for pretreatment, the water production rate of the system is higher than that of the system used alone, and the water production rate of the combined pretreatment mode is slowed down most, so as to stabilize the quality of the inlet water of the RO system. Therefore, the effect of the combined pretreatment mode for controlling the pollution blockage is more effective and stable and lasting, the pollution blockage rate of the RO system is slowed down, the pollution blockage condition of the reverse osmosis membrane is effectively relieved, and the running stability and running time of the RO system are increased, so that the service life of the reverse osmosis membrane is prolonged, the running cost of the RO system is reduced, and the combined pretreatment mode has important significance in the aspects of controlling the organic pollution blockage of the RO membrane and the like.
In the above 4 examples, if the determination method of the optimal dosing concentration is changed to: the adding concentration of the water treatment agent corresponding to the maximum DOC removal rate is selected as the optimal adding concentration, when the combined pretreatment mode is operated for 30 hours, the standardized water production rate is increased by about 16% -34% and 14% -53% compared with the case that the activated carbon and the ferric chloride are used independently, and the decreasing speed of the water production rate of the combined pretreatment is larger than that of the optimal adding concentration determination method adopted in the embodiment along with the prolonging of time, so that the optimal adding concentration determination method adopted in the embodiment is preferred.
The invention has the following beneficial effects:
(1) the invention creates a simple and feasible reverse osmosis membrane organic fouling control method, and makes up for the defect that the removal effect of a pretreatment method is not clear in the previous research;
(2) the method is suitable for removing soluble organic matters in reverse osmosis membrane inlet water, and can specifically reduce organic pollution blockage of the RO membrane;
(3) the invention is based on the pretreatment process of ferric chloride coagulation and activated carbon adsorption, and has the advantages of easily obtained raw materials and low cost;
(4) the method is simple and easy to implement and can adjust the adding proportion and the adding concentration of the ferric chloride and the activated carbon according to the characteristics of the water inlet sample.
The above embodiments are merely illustrative of various embodiments of the present invention, and the description is specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims (8)

1. The organic fouling control method of the reverse osmosis membrane is characterized by comprising the following steps:
(1) preparing two water treatment agents, namely ferric chloride stock solution and clean active carbon;
(2) taking an inlet water sample out of target inlet water of the reverse osmosis membrane, dividing the water sample into a plurality of parts, respectively adding activated carbon and ferric chloride to different concentrations, obtaining the removal rate of soluble organic carbon (DOC) in the corresponding water sample under different adding concentrations of the activated carbon and the ferric chloride, and determining the optimal adding concentration A of the activated carbon and the optimal adding concentration B of the ferric chloride according to the adding concentration and the DOC removal rate, wherein the adding concentration is the concentration of a water treatment agent in the water sample after the water treatment agent is added to the water sample; in the step, firstly, the optimal adding concentration ratio of the activated carbon and the ferric chloride is determined, and then the adding concentration of the ferric chloride is determined according to the optimal adding concentration ratio and the adding concentration of the activated carbon;
the method for determining the optimal adding concentration A and the optimal adding concentration B comprises the following steps:
(i) determining the optimal adding concentration ratio of the activated carbon and the ferric chloride in the water inlet sample according to the organic matter molecular weight characteristics and the three-dimensional fluorescence spectrogram characteristics of the water inlet sample, specifically measuring the molecular weight of the organic matter in the reverse osmosis water inlet sample, determining and obtaining the three-dimensional fluorescence spectrogram of the reverse osmosis water inlet sample, and judging whether the water sample has the molecular weight of 102-103Within Da range, there are obvious absorption peaks and within IV area and VI area in three-dimensional fluorescence spectrum there are two kinds of water sample characteristics of obvious fluorescence response; if the characteristics of the two water samples are both possessed, the optimal adding concentration ratio of the activated carbon to the ferric chloride in the water inlet water sample is determined to be 1: 1; if the water sample only has the characteristics of one water sample, determining that the optimal adding concentration ratio of the water sample to the water sample is 2: 1; if the characteristics of the two water samples are not possessed, determining that the optimal adding concentration ratio of the two water samples is 3: 1;
(ii) determining the initial DOC concentration value of the influent water sample as a0mg/L, determining the adding concentration interval of the activated carbon in the water inlet sample to be (3-9). alpha.0mg/L, and obtaining the DOC removal rate in the water sample under different active carbon adding concentrations;
(iii) determining the adding concentration interval of ferric chloride in the water inlet water sample according to the optimal adding concentration proportion determined in the step (i) and the adding concentration interval of the activated carbon in the step (ii), and obtaining the removal rate of DOC in the water sample under different adding concentrations of the ferric chloride;
(iv) according to DOC removal rates of different water treatment agents in (ii) and (iii) under different adding concentrations, selecting the corresponding adding concentration of the water treatment agent as the optimal adding concentration of the water treatment agent when the ratio of the increase rate of the relative DOC removal rate to the increase rate of the relative adding concentration of the water treatment agent is closest to 1;
(3) and (3) according to the optimal adding concentration of the activated carbon and the ferric chloride determined in the step (2), adding the activated carbon into the target inlet water to enable the concentration of the activated carbon in the target inlet water to be A, adsorbing for 0.5-1 hour, then adding the ferric chloride into the target inlet water to enable the concentration of the ferric chloride in the target inlet water to be B, and removing the activated carbon and the residual organic matters through coagulation.
2. The method for controlling organic fouling of a reverse osmosis membrane according to claim 1, wherein in the step (1), the preparation and storage method of the ferric chloride stock solution comprises the following steps: storing ferric chloride in a closed bottle, preparing a ferric chloride stock solution with the concentration of 1g/L at room temperature as a coagulant, and storing in a dark sealed manner after preparation.
3. The method for controlling organic fouling of a reverse osmosis membrane according to claim 1, wherein in the step (1), the preparation and storage method of activated carbon comprises the following steps: coconut shell granular activated carbon with the grain size of 1-2mm is adopted, the activated carbon needs to be repeatedly washed by water before being used until the dissolved organic carbon in the effluent of the washed activated carbon is lower than 0.5mg/L, and the clean activated carbon can be prepared; the clean active carbon is placed in an oven at 70 ℃ for drying, and then is placed in a beaker for light-tight sealing and storage.
4. The method for controlling organic fouling of a reverse osmosis membrane according to claim 1, wherein in step (2), the initial DOC concentration value in the influent water sample is determined to be a0mg/L, determining the adding concentration of a water treatment agent in the water inlet sample as biThe corresponding DOC concentration value at mg/L is aimg/L, the adding concentration of the water treatment agent is biDOC removal rate c corresponding to mg/LiComprises the following steps: (a)i-a0）/a0。
5. The method for controlling organic fouling of a reverse osmosis membrane according to claim 4, wherein the DOC concentration is measured in step (2) by: 5ml of water sample to be detected is taken, and the DOC concentration in the water sample is determined by using a TOC analyzer after the water sample passes through a 0.45 mu m filter membrane.
6. The method for controlling organic fouling of a reverse osmosis membrane according to claim 1, wherein in step (2), the method for determining the optimum dosing concentration comprises: selecting the corresponding water treatment agent adding concentration as the optimal adding concentration when the ratio of the increase rate of the relative DOC removal rate to the increase rate of the relative water treatment agent adding concentration is closest to 1, and assuming that two adjacent adding concentrations of the same water treatment agent are respectively bi-1、bi（bi>bi-1) The respective DOC removal rates are ci-1、ciIf the adding concentration of the water treatment agent is biWhen the DOC removal rate is increased, the DOC removal rate is (c)i-ci-1）/ci-1The increase rate of the addition concentration of the water treatment agent is (b)i-bi-1）/bi-1。
7. The organic fouling control method of a reverse osmosis membrane according to claim 1, characterized in that in step (2), the adding concentration interval of activated carbon and ferric chloride is determined first, and then the optimal adding concentration is determined in the adding concentration interval;
the determination method of the adding concentration interval comprises the following steps: determining the initial DOC concentration value in the influent water sample as a0mg/L, the adding concentration intervals of the activated carbon and the ferric chloride are respectively (3-9). alpha.0mg/L and (1-9) × a0mg/L。
8. The method for controlling organic fouling of a reverse osmosis membrane according to claim 7, wherein in step (2), the activated carbon is added at a concentration of 3a0mg/L、4.5a0mg/L、6a0mg/L、7.5a0mg/L、9a0mg/L。
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